Financial Instruments (Tables)

6 Months Ended

Jun. 30, 2019

Financial Instruments

Schedule of available-for-sale securities

	June 30, 2019								December 31, 2018
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Estimated Fair Value		Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Estimated Fair Value
	(in thousands)
Money market deposits	$	630	$	—	$	—	$	630	$	26,539	$	—	$	—	$	26,539
U.S. Treasury securities		158,429		733		(65)		159,097		76,061		29		(405)		75,685
U.S. agency securities		13,004		—		(27)		12,977		13,017		—		(126)		12,891
Municipal securities		35,825		162		(8)		35,979		18,935		7		(57)		18,885
Total	$	207,888	$	895	$	(100)	$	208,683	$	134,552	$	36	$	(588)	$	134,000
Classified as:
Cash equivalents							$	630							$	26,539
Short-term investments								208,053								107,461
Total							$	208,683							$	134,000

Summarized portfolio of available-for-sale securities by contractual maturity

	June 30, 2019
	Amortized Cost		Fair Value
	(in thousands)
Less than one year	$	97,180	$	97,276
Greater than one year but less than five years		110,077		110,777
Total	$	207,257	$	208,053